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Thread: R90 Brake help / question

  1. #1
    drpetecrocker
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    R90 Brake help / question

    The front brakes are squeaking severely. Looking at the pads, it appears that they need to be swapped out. Also, the rotor has a bit of grooving in it and is fairly glazed. Also, it is a pretty hard pull to slow the bike rapidly. I have been told this is somewhat to be expected.

    Is it possible to re-surface the rotor? Do I need to do that, or should I just replace the brake pads? Or do I need to replace the rotor and pads?

    Thanks!

    Some pics:




  2. #2
    copandengr
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    Rotor

    In my opinion, the pads that were on the bike at one time were of inferior quality. This has caused the galling of the rotor. I believe the rotor needs to be resurfaced, provided there is sufficient thickness left to do so. NEVER go beyond the minimum thickness that is marked on the rotor.

    Also, the galling is going to contribute in no small way to the squealing you mentioned. A proper rotor surface will increase braking power, and the pads will last longer and be less likely to glaze.

    Looking closely at the photos, it appears there is significant wear on the rotor. You would probably be money ahead if you replace it.

  3. #3
    drpetecrocker
    Guest
    Quote Originally Posted by copandengr View Post
    In my opinion, the pads that were on the bike at one time were of inferior quality. This has caused the galling of the rotor. I believe the rotor needs to be resurfaced, provided there is sufficient thickness left to do so. NEVER go beyond the minimum thickness that is marked on the rotor.

    Also, the galling is going to contribute in no small way to the squealing you mentioned. A proper rotor surface will increase braking power, and the pads will last longer and be less likely to glaze.

    Looking closely at the photos, it appears there is significant wear on the rotor. You would probably be money ahead if you replace it.
    That's what I suspected. I need to get a new battery for my caliper to measure the thickness. Who resurfaces these things anyway? Can an auto parts store do it?

    The guys at motoghost recommended an aftermarket rotor that costs $200. I can't remember the name. Does anyone have any experience with aftermarket rotors?

  4. #4
    Liaison 20774's Avatar
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    IIRC, rotors are pretty close to min thickness when new. I doubt they can be turned in the classic way. Possibly using some kind of surface grinding might work.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    Very difficult to find someone that will or can turn ss rotors - they sure do look like they are toasted.

    Based on my recent complete overhaul I would absolutely recommend staying OEM. I used aftermarket pads (Lucas/TRW) and got to pay the price in terrible braking and a "do over' from poor tolerances in manufacturing.

    Chicago BMW has special airhead pricing on parts, (20% discount but don't tell anyone) just ask for it!

  6. #6
    copandengr
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    Thickness

    If you are referring to a caliper in the conventional sense it is unlikely to give you an accurate measurement of the thickness. The reason would be the unworn outer edge of the rotor would prevent the caliper from getting to the center of the wear pattern. A micrometer would be the choice of a measuring tool. You could place a penny on each side of the rotor and then deduct the thickness of the pennies, but this will not take into account the amount of metal that will have to be removed since the galling appears rather deep to my eyes.

    Stainless steel is difficult to machine, especially when it is of a larger diameter relative to its thickness. A cutting tool will simply force the rotor to flex away from it. Surface grinding would be of little help because if the rotor is warped, the grinding process will only amplifiy the problem. Tool post grinding could also be done, but this would be very costly as well.

    An automotive brake shop will not be able to resurface this. Their lathes are designed to hold in place a conventional automotive disc or drum, not one with such a large diameter center. If you get the chance to observe an auto disc lathe in action, it utilizes two cutting tools, one on each side. This is how the flexing is eliminated. A machine shop could set up a regular lathe to do this, but the cost would be prohibitive.

    I also agree that most European rotors are manufactured with very little "extra" metal for resurfacing, and many of the car makes specifically prohibit resurfacing rotors. Volvo is one of them for instance.

    Bite the bullet and install a new rotor and pads. Just make sure the rotor and pads are made to OEM specs and are not a copy made of chineseium.

    One of my favorite lines re brakes was from an issue of Cycle World when Kawasaki came out with the Mach III yet still had a drum brake on it. The article said "go fast bikes need stop fast brakes". Brakes are no place to try to get by cheaply.

  7. #7
    Quote Originally Posted by RonKMiller View Post
    Chicago BMW has special airhead pricing on parts, (20% discount but don't tell anyone) just ask for it!
    Is that 20% off the price on their website?

    Brian

  8. #8
    drpetecrocker
    Guest

    Ebc?

    Motoghost recommends EBC pads and rotor. They have a price of $200 for the rotor and $45 for the pads. This rotor is drilled, and according to them has a higher coefficient of friction. Anyone have any experience with this product?

  9. #9
    Liaison 20774's Avatar
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    Quote Originally Posted by drpetecrocker View Post
    Anyone have any experience with this product?
    Search this forum for "EBC". There's a ton of hits...
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  10. #10
    Registered User jad01's Avatar
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    I installed a set of EBC rotors and pads on my R80/7 last year & really like them alot. The rotors are fully floating (and thus more resistant to warping), and when matched to the EBC pads, are quiet and offer good stopping power. I definitely like them better than the stock rotors in terms of how smooth they feel in use. I had upgraded to dual disks from a single disk the year prior (using good stock rotors), which offered better stopping power. Later I switched to the EBC rotors, and they are just better- smoother & quieter- I'd be reluctant to go back...
    Jim
    '78 R80/7 and '84 R100RS (Blues Brothers), '86 K75C (Icy Hot)
    '90 and '93 Mazda Miatas (Jelly Bean and Red Hot), '97 Nissan XE PU (Mighty Mouse)
    '96 Giant Upland (big Kendas, baby!)

  11. #11
    On the Road
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    Toast

    As others have already stated your rotor looks "toasted" I do not believe you could ever turn it since too much material is already gone. A micrometer with a point on the end could get into the trough that exists on your rotor surface. A standard micrometer will measure the peaks unless the groove is wider than the micrometer faces. I just replaced my pads with EBC and am very happy with them. Looks like a fresh start/ rotor & pads/ would suit you well.

  12. #12
    mymindsok
    Guest
    Brand new BMW rotors are two thin to turn, so when the get warped or become grooved past usage, the solution is to replace with new or good-used parts.

    Remember, that solid disk dates back to 1974!!

  13. #13
    drpetecrocker
    Guest

    Thanks. EBC for me.

    Ok, that's it. I'm going with EBC. Thanks for all the input. I was a little reluctant to get away from the stock look, but I bought this bike to ride it, not just look at it.

  14. #14
    Registered User toooldtocare's Avatar
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    Since you are no longer going stock, here is another option-floating rotors with ceramic pads. Photo of front brake. Brand is "Brake" and is the semi-floating version. They work much better than the stock brakes.
    Attached Images Attached Images

  15. #15
    Registered User stanley83's Avatar
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    Floating Rotor Source?

    Quote Originally Posted by toooldtocare View Post
    Since you are no longer going stock, here is another option-floating rotors with ceramic pads.
    Who sells these? Google search has been fruitless so far.

    Thanks,
    Justin

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